Metro serves a tiny fraction of N. VA. Sure, if you're in DC and commuting out, it's probably ok, but people don't tend to stay in DC very long. Once they have kids and realize there is no hope of reasonable public education there, they move.
Your comment about "nobody lives near a metro line" though - I mean, come on! With the orange line and silver line extension there are lots of places in NoVa near the metro. Yes, the car traffic is horrible, but the car traffic is horrible in SF, LA, Boston, NY, Austin...
As another commenter pointed out, there is actually a ton of empty real estate in Crystal City itself and no doubt a ton of it will be built up as apartments/condos now.